3.9.6 Autoradiography

Autoradiography can provide information about the nature of the contamination, e.g., whether it is homogenous or particulate, or both. Moreover, the combination of different techniques has the potential for identifying the particulate contamination as being that of uranium, plutonium, or fission products. If the detected particles are sufficiently large in size (> 20 µ), further investigations can be made to elucidate the physical/chemical and isotopic characteristics of the particles.

Autoradiography is based on the simple blackening of a sensitive film. After the exposure to radiation, the film is developed and shows a blackening where it has been exposed. Commercially available X-ray film (e.g., Kodak AG7) is suitable for the detection of fission products in samples obtained from different soil layers, ashed biota, air filters, etc. The limit of detection for a point source for film exposed overnight is typically equal to about 0.1 Bq of 137Cs.